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Full text of "Electrical Discharge between Concentric Cylindrical Electrodes"

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June 2, 1916] 



SCIENCE 



787 



tions prevailing in the island, and at least not 
better adapted than the species from which 
they sprung. Or, in other words, that they 
did not originate in advantageous response to 
those local conditions. A large amount of facts 
and considerations has been brought forward 
by the author in order to justify this conclu- 
sion. 

These conclusions provide us with a strong 
argument against the hypothesis of a slow and 
gradual evolution by small and almost invisible 
steps, and for the theory of their production 
by mutations. In the rare cases of rapid dis- 
persal of new species a better adaptation may 
of course be assumed as one of the chief factors, 
but on the average the dispersal is very slow 
in the beginning, giving no argument in favor 
of this view. 

Furthermore these considerations lead to the 
view that wide distribution and commonness 
are chiefly dependent on age, and only rarely 
on adaptation. In every family the genera 
with the widest distribution may be considered 
as the oldest, those with a smaller domain as 
younger, and the local endemics as the young- 
est of all. These principles will be used in sub- 
sequent studies to draw pedigrees of families. 
But the studies made by the author up to this 
time go to show that nearly all families have 
the same general type of distribution, that 
evolution of forms is on the average indiffer- 
ent, and that most of the so-called adaptations 
are of no special advantage to their possessors. 

Another argument relates to the possible 
size of mutations. It is often assumed that 
mutations must of necessity be small, consider- 
ing that it seems probable that only one unit- 
factor will be changed at a time. This con- 
ception seems to the author to be an unneces- 
sary handicap to the theory of mutation and 
he proposes that it should be replaced by the 
hypothesis that no specific change is too great 
to appear in one mutation. The difference be- 
tween endemic species of Ceylon and their 
nearest allies is often very large, as may be 
deduced from the fact that they are accepted 
as well-marked Linnean species by such author- 
ities, as Trimen and Hooker. But in many 
cases they are even larger. For instance, 



Coleus elongatus, which occurs only on the top 
of Ritigala and here only in about a dozen of 
individuals, differs so much from all other 
Gdlei, that it may well be regarded as sub- 
generically distinct. And for the 17 endemic 
genera, which have only one species each, it 
seems at least very probable that the whole 
genus has arisen at a single step. 

In concluding I might state that my own 
studies on the production of new forms among 
the (Enotheras have of late led me to the con- 
clusion that mutations are in many cases of a 
far more complicated nature than has been 
assumed until now. Many of them, as for in- 
stance the production of 0. ruhrinervis, 0. 
nanella and 0. gigas, involve the simultaneous 
change of two or more characters, in some 
cases of quite a large number of unit-factors. 
Why these changes should so regularly go to- 
gether, we do not, as yet, know, but the fact 
goes to increase the analogy between the ex- 
perimental mutations of these plants and the 
mutations in the wild condition of the Ceylon 
endemics. 

Prom the facts adduced by Willis, and re- 
viewed in this article, it seems obvious that 
the parallelism of natural and experimental 
mutations is a very close one. 

Hugo de Vbies 

electrical discharge between concen- 
tric cylindrical electrodes 

In operating vacuum tubes we invariably 
use an induction coil or an electrostatic ma- 
chine. The discharge in either case is never 
quite steady and hence these methods of opera 
tion do not lend themselves well to a critical 
study of the growth of the cathode dark 
spaces. A steady, and of course continuous, 
discharge may be had if the current is drawn 
from a high potential storage battery. Ordi- 
narily it takes more cells than are available; 
however, by a right choice of conditions a 
rather extended study may be made with di- 
rect current potentials of less than 1,000 volts. 
The following experiments with concentric 
cylindrical electrodes were performed recently 
by the writer in class demonstration. 

The discharge vessel consists of an ordinary 



788 



SCIENCE 



[N. S. Vol. XLIII. No. 1118 



three-quart battery jar. A hole bored through 
the bottom receives the evacuating tube, the 
junction being made airtight with ordinary 
sealing wax. The lip of the jar is ground flat 
to receive the plate glass lid. The junction 
here is made by means of the frequently used 
half-and-half wax, beeswax and resin. This 
wax because of its low melting point admits 
of easy removal of the glass plate. The elec- 
trodes are concentric cylinders and may well 
be made of sheet aluminum — one electrode to 
fit snugly the inner wall of the jar, and the 
other mounted on a cylinder of glass tubing 
about 1J inches in diameter, which in turn is 
supported accurately concentric by sealing 
wax from the bottom of the jar. Outside con- 
nections to the electrodes are made by fine 
bare copper wire run out through the waxed 
joints. The assembled discharge vessel is 
shown at a in Pig. 1. 



To pomp 




Fig. 1. 

The vessel may be exhausted by a Gaede 
mercury or a Gaede piston pump and, if de- 
sired, the vacuum carried farther by the use 
of charcoal and liquid air, though the latter is 
-not necessary. The potential employed by 
the writer to produce the discharge was fur- 
nished by a cabinet of high potential storage 
cells of 1,000 volts. 

Two methods of operating were employed. 
In the first an adjustable water resistance is 
connected in series with the cells and dis- 
charge vessel as shown at b in Fig. 1. When 
the vacuum is right a beautiful discharge will 



make its appearance as patches of light on the 
electrodes. These patches of light, when there 
is considerable resistance in the circuit and 
the vacuum is not very high, will be opposite 
each other and the discharge, as a whole, will 
wander about, sometimes swinging entirely 
around, or at times travelling to the edges of 
the electrodes, only to break away and move 
to some other point. The movement of the 
cathode glow (which is the smaller and hence 
the brighter) is similar to that of the cathode 
star over the surface of mercury in a mercury 
vapor lamp. These areas grow as the vacuum 
improves when ultimately the entire surface 
of each electrode is covered. Or, with the 
vacuum kept constant, the areas may be made 
to increase in size by cutting out resistance. 
Hence by improving the vacuum and at the 
same time cutting out resistance the dis- 
charge, if the inner cylinder is made cathode, 
grows rapidly into a brilliant bull's-eye. The 
appearance is very realistic, for if now resist- 
ance is cut in, the dark space around the 
cathode (as is evident after a moment's re- 
flection) grows smaller, and vice versa. Its 




Fig. 2. 

outline is exceedingly sharp and perfectly 
steady, and yet, though the discharge appears 
very brilliant, the current required may not 
exceed 20 milliamperes. 

This form of discharge vessel offers an in- 
teresting method for the study of the stria- 
tions and their relative spacing with reference 
to the impressed discharge potentials. These 
effects are best shown when the vacuum is not 
too high and the discharge potential is ad- 
justed to give a patch on the cathode, which 



June 2, 1916] 



SCIENCE 



789 



we will take as the inner cylinder, of about 
one square centimeter in area. Under these 
conditions the Faraday dark space should be 
about 8 mm. in length, and the Crookes dark 
space should be just visible between the vel- 
vety cathode glow and the cathode electrode. 
Another prerequisite is that the discharge 
must not cling to the edge of the aluminum 
electrodes, but should occupy some intermedi- 
ate position as shown at 1 in a, Fig. 1. In this 
position the characteristics of the discharge 
are shown with exceeding clearness. If now 
some additional resistance is cut in, the area 
of the discharge will become less, the Fara- 
day dark space will shorten, the positive col- 
umn will move towards the cathode, and the 
number of strise in it will increase, the extra 
strias being, as it were, drawn out of the anode. 
The configuration is perfectly steady except 
that the discharge, as a whole, is liable to 
wander. This transition may be continued by 
a still further increase of the resistance in the 
circuit, the dark space becoming ever shorter, 
the positive column lengthening and at the 
same time shrinking in area and the striae in- 
creasing in number, all without loss of out- 
line or brightness. Finally, the discharge will 
cease. The various stages are suggested at 1, 
2, 3 in h, Fig. 1. 

In the second method the discharge vessel 
with its commutator is placed in a derived 
circuit (Fig. 2). This arrangement enables the 
discharge potential to be continuously varied 
over a wide range, and hence for a given 
vacuum the relation between the length of the 
dark space and the impressed voltage may be 
exhibited. Again this arrangement enables 
the minimum potential -to be readily deter- 
mined that will maintain a discharge. As an 
example, for a given vacuum with the resist- 
ance AG equal to 1/3 that of AB the discharge 
was observed to just pass, indicating that the 
potential necessary was 330 volts. 

Additional phases of the experiment will 
suggest themselves to the operator. 

Chas. T. Knipp 

Laboratory op Physics, 
University op Illinois, 
March 4, 1916 



UTAH ACADEMY OF SCIENCES 

The ninth annual convention of the Utah Acad- 
emy of Sciences was held in the chemistry lecture 
room of the University of Utah. Three sessions 
were held: one at eight p.m., Friday, April 7, one 
at ten A.M., Saturday, April 8, and the closing ses- 
sion at two p.m. of the same day. Dr. Harvey 
Fletcher presided at all of the sessions. 

Dr. E. G. Peterson, U. A. C, and Professor 
Carl P. Eyring, B. Y. U., were elected to fellow- 
ships in the academy. The following were elected 
members: Professor George B. Caine, U. A. ft, 
Dean Milton Bennion, U. U., Professor Newton 
Miller, U. U., Professor A. L. Matthews, U. U., 
Dr. George S. Snoddy, U. U., Miss Hazel L. 
Morse, East High School, Salt Lake City, C. Ar- 
thur Smith, East High School, Salt Lake City, C. 
Oren Wilson, East High School, Salt Lake City, 
Professor Estes P. Taylor, U. A. ft, Dr. A. P. 
Henderson, B. Y. U., and Edgar M. Ledyard, Salt 
Lake City. 

Captain Francis Marion Bishop, a companion of 
Major Powell in his famous explorations of the 
Uinta Mountains, was elected to honorary life 
membership. 

The following officers were elected for the en- 
suing year: 

President — Dr. Frank Harris, U. A. ft, Logan. 

First Vice-president — Dr. L. L. Daines, U. U., 
Salt Lake City. 

Second Vice-president — Professor Carl F. Ey- 
ring, B. Y. U., Provo. 

Councillors — Dean J. L. Gibson, U. U., Dr. W. 
E. Carroll, U. A. ft, W. D. Neal, Salt Lake City. 

The following lectures and papers were pre- 
sented: 

' ' Industrial Eesearch in U. S. A., ' ' by Dr. Har- 
vey Fletcher, B. Y. U. 

"The Alkali Content of Certain Utah Soils," by 
Dr. Frank S. Harris, U. A. C. 

"The Agricultural College and Scientific Ee- 
search," by Dr. E. G. Peterson, U. A. C. 

"Selecting Holstein-Friesian Bulls by Perform- 
ance," by Dr. W. E. Carroll, U. A. ft 

"Peyote, an Indian Narcotic," by A. O. Gar- 
rett, East High School, Salt Lake City. 

' ' An Epidemic of Colds with Micrococcus catar- 
rhalis as Causative Agents, ' ' by Dr. L. L. 
Daines, U. U. 

"The First Becorded Case of Babies in Utah," 
by Dr. L. L. Daines, U. U. 

"Botulinus Poisoning from a Vegetable 
Source, ' ' by Dr. L. L. Daines, U. U. 

"Comparison of Methods of Treatment for